Project Summary The early development of a number of mammalian tissues including the eye depends in part upon the activity of an evolutionarily conserved regulatory circuit that includes members of the Pax, Six, Eya and Dach gene families. Of particular interest to this proposal is the role that the Six and Eya proteins play during retinal specification. The function of these gene families are highly significant as mutations in select genes can lead to holoprosencephaly, bilateral anophthalmia, congenital cataracts as well as non-retinal defects such as myotonic dystrophy and branchio-oto-renal syndrome. Furthermore, these genes are also implicated in tumorigenesis and numerous cancers. Six proteins serve as homeobox containing transcription factors while Eya proteins function as transcriptional co-activators and as protein tyrosine phosphatases. These protein families cooperate by forming Six-Eya heterodimers that are thought to function as strong activators of downstream target genes. The activity of these heterodimers is crucial as loss-of-function mutations can lead to retinal defects in human patients and mouse model systems as well as total elimination of the compound eyes of the fruit fly, Drosophila melanogaster. The association of Six and Eya gene lesions with retinal disorders in both insect and mammalian systems provides us with an exciting opportunity to further explore the roles that these factors play in retinogenesis. The developing eye of the fruit fly has become a premier model system for studying the genetic and molecular mechanisms that govern tissue determination. The advantages include a stereotyped mode of development that has been well described, a large body of experimental data on known eye specification genes and a vast array of available mutant strains and molecular/cellular markers. In Drosophila, eyes absent is the sole member of the Eya family while sine oculis, optix and DSix4 represent the Six gene family. Despite the significant efforts that have been placed on understanding the roles that these genes play in development there are a large number of important questions that still remain unanswered. The goals of the proposed work are to address these questions and provide answers that will further our understanding of role played by Six and Eya genes in retinal determination. Among the outstanding issues that we will address are (1) the role that optix plays in normal eye development;(2) the functional and biochemical similarities and differences that exist amongst the fly and mammalian Six proteins;(3) the role that sine oculis plays in cell proliferation and the cell cycle;and (4) the potential role for sine oculis and eyes absent in developing photoreceptor cells. In order to address these issues we will use a creative mixture of genetic, molecular and biochemical approaches along with genomic and bioinformatic methods to investigate these issues.